Separation Processes Questions and Answers - Rate Based Method for Packed Columns Part-1

1. What are the actual numbers of required plates when the overall stage efficiency is 0.7 and the calculated equilibrium stages are 2.8?
a) 2
b) 4
c) 5
d) 7

Answer: b
Explanation: By E o = Nt /N a , N a = 2.8/0.7=4.

2. What are the actual numbers of required plates when the overall stage efficiency is 0.6 and the calculated equilibrium stages are 4.8?
a) 8
b) 3
c) 5
d) 7

Answer: a
Explanation: By E o = Nt /N a , N a= 4.8/0.6=8.

3. What is the overall stage efficiency if the calculated equilibrium stages are 8 and the actual plates required are 12?
a) 0.75
b) 0.6
c) 0.56
d) 0.12

Answer: a
Explanation: By E o = Nt /N a , E o = 8/12 = 0.75

4. What is the overall stage efficiency if the calculated equilibrium stages are 9 and the actual plates required are 11?
a) 0.75
b) 0.82
c) 0.56
d) 0.12

Answer: b
Explanation: By E o = Nt /N a , E o = 9/1 = 0.82.

5. What is the overall stage efficiency if the calculated equilibrium stages are 7 and the actual plates required are 13?
a) 0.75
b) 0.6
c) 0.54
d) 0.12

Answer: c
Explanation: By E o = Nt /N a , E o = 7/13 = 0.54.

6. Packed columns are better analyzed by:
a) Mass transfer coefficients
b) Equilibrium stage methods
c) Graphical methods
d) Algebraical methods

Answer: a
Explanation: Packed columns are better analyzed by mass transfer coefficients.

7. What is the formula for HETP or HETS?
a) HETP = l T *N T
b) HETP = l T-N T
c) HETP = l T /NT
d) HETP = lT+NT

Answer: c
Explanation: The formula for HETP is HETP = lT/NT where lT is the packed height length and the N T is the number of equilibrium stages.

8. At the interface of liquid and vapor, which interface exists?
a) Chemical
b) Physical
c) Thermal
d) No equilibrium exists

Answer: b
Explanation: At the interface of liquid and vapor, a physical equilibrium exists.

9. Which of the following is the correct illustration of rate of mass transfer?
a) r= ky a(y-y 1 ) =kx a(x-x 1 )
b) r= ky a(y 1 -y) =kx a(x 1 -x)
c) r= ky a(y-y 1 ) =kx a(x 1 -x)
d) r= a(y-y 1 ) =a(x 1 -x)

Answer: c
Explanation: r= k y a(y-y 1 ) =k xa(x 1 -x) is the correct illustration for rate of adsorption where kya and k x a are volumetric mass transfer coefficients.

10. Which of the following is the correct representation of overall mass transfer coefficient?
a) 1/Ky a = 1/ky a +K/Kx a
b) 1/Ky a = 1/ky a +K/Ky a
c) 1/Ky a = 1/ky a +1/KKx a
d) Ky a = 1/ky a +K/Kx a

Answer: a
Explanation:The correct representation of overall mass transfer coefficient is 1/K y a = 1/k y a +K/K x a, where K y is the overall mass transfer coefficient obtained from slope=point form.